1. Field of the Invention
The invention relates to a method for plasma treatment of containers and to a device for plasma treatment of containers.
2. Description of Related Art
Such methods and devices are, for example, used to provide plastics with surface coatings. In particular, such devices are already known for coating inner or outer surfaces of containers which are provided for the packaging of liquids. Devices for plasma sterilisation are also known.
A plasma chamber for the internal coating of containers made from PET is described in publication W095/22413 A1. The containers to be coated are lifted by a movable floor into a plasma chamber and connected to an adapter in the region of a container mouth. An evacuating of the container interior can be effected through the adapter. A hollow gas lance is also introduced through the adapter into the interior of the containers in order to supply process gas. The plasma is ignited using a microwave.
The arranging of a plurality of plasma chambers on a rotating wheel is also already known from this publication. A high rate of production of containers per unit of time is assisted in this way.
Publication EP 10 10 773 A1 describes a feeding apparatus in order to evacuate the interior of a bottle and supply it with process gas. WO 01/31680 A1 describes a plasma chamber into which the bottles are introduced by a movable cap which has previously been connected to a mouth region of the bottles.
Publication WO 00/58631 A1 also already shows the arrangement of plasma stations on a rotating wheel and describes, for such an arrangement, a group-by-group allocation of vacuum stages and plasma stations in order to assist a favourable evacuation of the chambers and of the interiors of the bottles. It also mentions the coating of a plurality of containers in a common plasma station or common chamber.
Another arrangement for performing an internal coating of bottles is explained in publication WO 99/17334 A1 which describes in particular an arrangement of a microwave generator above the plasma chamber as well as a vacuum and operating media supply line passing through a floor of the plasma chamber.
DE 10 2004 020 185 A1 describes a gas lance which can be introduced into the interior of a preform which is to be coated, and is used to supply process gases. The gas lance is positionable in the longitudinal position of the container.
With the majority of known devices, plasma-generated container coatings of silicon oxides having the general chemical formula SiOx are used to improve the barrier properties of the thermoplastic material. Such barrier coatings, especially on the inner wall of a container interior, prevent a penetration of oxygen into the packaged liquids as well as an escape of carbon dioxide in the case of carbonated liquids, and so improve the storage properties and/or the long-lasting shelf life of the liquids that are filled and/or packed in the container.
In a customary device configuration for plasma treatment, n treatment segments are arranged on a plasma wheel in corresponding angular sections, with each treatment segment comprising a plasma station having at least one or a plurality of evacuable plasma chambers which in turn have one or a plurality of treatment places for container treatment. Two or four treatment places for example are arranged in each plasma chamber or in the chamber interior so that consequently n times 2 or n times 4 treatment places in all circulate on a plasma wheel for the aforesaid device types.
With the plasma chamber of a treatment segment being open, the one container or the plurality of containers is/are guided in or guided out together in a loading or unloading step, it being possible for this to be effected either simultaneously or slightly staggered for the individual containers. A plasma station is usually provided as a unit in a treatment segment so that in a loading or unloading step all containers are guided into or out of the plasma station together analogously. In its simplest configuration therefore, a treatment segment incorporates a plasma station having a plasma chamber which comprises a chamber interior in which a treatment place for a container is arranged.
In case of the known methods and devices for plasma treatment, it is customary for the process gas that is introduced into the plasma chamber of a corresponding plasma station to be supplied from a central process gas supply unit which interacts with all plasma stations—or their treatment places—that are arranged on a wheel of the plasma module.
In the event of an operational malfunction, i.e. in particular a breakdown, occurring at one or a plurality of plasma stations or treatment places of the plasma module therefore, in the prior art the process gas supplied for this corresponding plasma station is distributed among the remaining intact plasma stations of the plasma module. This in turn leads to an unwanted increased throughput of process gas at the remaining plasma stations which are intact and hence not subject to any operational malfunction, and therefore ultimately to a negative influence on the quality of the barrier coatings on the inner wall of the containers.